The threat arrived, as so often in transatlantic politics, in a few angry lines and an off‑the‑cuff remark. Donald Trump, now back in the White House, has openly mused about pulling the United States out of NATO, furious that European allies refused to join US operations to secure the Strait of Hormuz and support the wider war against Iran. What once would have been dismissed as bluster now feels uncomfortably plausible. The question is no longer just whether America “can” leave the alliance. It is what kind of Europe – and what kind of citizen-state relationship – would emerge on the other side.
From Hormuz to Brussels: A crisis of expectations
When Washington called for European ships and planes to help secure the vital chokepoint of Hormuz, the answer in most European capitals was a carefully worded “no.” Leaders argued that NATO is a defensive alliance, designed to protect the North Atlantic area, not to underwrite another US-led campaign in the Middle East. For them, tying NATO directly to a war with Iran risked escalation, domestic backlash and legal questions at home.
In Washington, the refusal cut deeper than a single operation. It reinforced a long‑standing American grievance: that NATO allies expect US troops and taxpayers to stand guard over Europe’s borders, but hesitate when the United States asks for help beyond them. In Trump’s framing, it is a one‑way guarantee – Europeans get Article 5, Americans get lectures. Whether one accepts that narrative or not, it feeds a political mood in which a radical step – leaving NATO – can be sold as overdue tough love rather than geopolitical vandalism.
The legal trapdoor under NATO
International law offers a surprisingly simple escape hatch. Article 13 of the North Atlantic Treaty allows any member to withdraw one year after giving formal notice. There is no arbitration panel, no penalty clause, no requirement for consensus. If Washington notified its intention to leave, the treaty, as a matter of international law, would simply let it go.
But law never lives in a vacuum. Inside the United States, withdrawal is a constitutional minefield. The US system is built on shared powers, and while presidents negotiate and sign treaties, the Senate must ratify them. The Constitution says nothing explicit about who has the power to “unmake” a treaty. Previous presidents have terminated agreements unilaterally, but mostly in lower‑stakes contexts and without serious congressional pushback.
With NATO, Congress has tried to slam that door shut. In recent years, defense authorization laws have included provisions stating that a president may not withdraw from NATO without Senate approval or an act of Congress. Trump, or any president who wanted to leave, would have to choose: comply and seek that approval – almost certainly doomed – or defy Congress and plunge the country into a constitutional battle. Courts, which often avoid stepping into foreign‑policy disputes, might be forced to answer a question they have dodged for decades: can a president walk away from a cornerstone alliance over Congress’s objection?
In other words, from the outside NATO looks like a voluntary club. From the inside, US membership has become a test case for separation of powers.
The morning after: A Europe without the American umbrella
Imagine, nonetheless, that the legal hurdles are cleared. A year after notice is given, the United States formally leaves NATO. The alliance is not abolished on paper – the treaty would still bind the remaining members – but its military and psychological core would be gone.
For European governments, the shock would be immediate and brutal. NATO’s integrated command structure, its planning, logistics, strategic airlift and much of its high‑end capability are American. Without them, Europe would face three unsatisfying options at once.
First, scramble to build a genuinely European defense architecture – perhaps by turbocharging the EU’s timid security structures, or creating a new treaty among willing states. That would take money, time and political courage, and it would come with hard domestic conversations about conscription, defense spending and industrial policy.
Second, try to reinvent the relationship with Washington as a web of looser, ad‑hoc coalitions. Europe might still fight alongside the United States in some crises, but without the predictability of a treaty, every operation would be a negotiation. For smaller states on NATO’s eastern flank, that uncertainty could be existential.
Third, quietly accept a higher level of risk. Authoritarian powers – would immediately test the edges of Europe’s security order, probing cyber defenses, political cohesion and, perhaps, territorial red lines. Deterrence is not just about tanks and missiles; it is about the perceived will to use them. A NATO without the United States would have to prove its will from day one.
NATO’s remaining members would keep the treaty’s famous Article 5 among themselves, but the atmosphere would change. An alliance founded on the motto “an attack on one is an attack on all” would suddenly feel conditional, fragile, maybe even temporary.
Germany’s quiet revolution: Freedom of movement meets mobilization
This is where Germany’s new rule, largely overlooked outside specialist circles, becomes more than a bureaucratic tweak. Berlin has introduced a requirement that men aged 17 to 45 who reside in Germany must obtain special permission from military authorities if they want to stay abroad for more than three months. On paper, it is an administrative measure linked to conscription law. Politically, it is something else: a subtle redefinition of the relationship between citizen and state.
For decades, Europeans have gotten used to a borderless continent where young people float between Erasmus semesters, gig work in another capital and extended travels without much thought. The German rule draws a line under that carefree assumption – at least for a specific group. It does not ban travel. But it says, in effect: if you are a military‑eligible man, you may not simply disappear from the state’s reach for long periods without asking.
The logic is brutally straightforward. In a world where large‑scale war once again feels thinkable, a government that might need to mobilize quickly cannot afford to lose track of its potential draftees and reservists. An exit‑permission regime is a legal tool to ensure that, when the call comes, the state knows where you are – and has pre‑emptively asserted its right to recall you.
There is a civil‑liberties cst. Freedom of movement is curtailed not because of individual wrongdoing, but because of age, gender and hypothetical future needs. Dual nationals and migrants who have made Germany their home may find that the openness that attracted them now comes with strings attached.
The invisible thread between Washington and Berlin
Officially, Germany’s move is not a reaction to Trump’s threats over NATO. It is framed as part of broader Bundeswehr reforms and the modernization of conscription law. Yet it is hard to miss the timing and the deeper trend. Across Europe, governments are quietly reversing assumptions that guided policy since the end of the Cold War: that large wars are unlikely, that conscription is outdated, that citizens are primarily individual rights‑holders, not a potential mobilization pool.
Here the NATO debate and the exit‑permit rule intersect. If America’s commitment to Europe becomes negotiable, European states will feel compelled to rely more heavily on their own populations – and to do so, they will use law. Not just in terms of higher defense budgets or new weapons procurement, but in more intimate ways: who can leave, where they can go, how quickly they can be summoned back.
In the United States, the likely battleground is institutional – president versus Congress, treaty law versus domestic statutes. In Europe, and particularly in Germany, the battleground is the body and the passport. The US may fight over whether it owes protection to allies. Europeans may increasingly argue over what they owe their own states.
The symbolism matters. For a generation, the story Europe told itself was one of ever‑expanding liberties: movement, study, work, marriage, identity. The German rule carves out an exception for security, and does so not in a declared emergency but in peacetime. It normalizes the idea that, beneath the everyday freedom to hop on a cheap flight, there is a layer of obligation that can be switched on through ordinary legislation.
A fractured West looks in the mirror
Taken together, Trump’s threat to walk away from NATO and Germany’s new exit‑permission regime sketch a portrait of a West that no longer takes its own order for granted. The United States questions whether defending Europe is worth the cost when allies balk at following it to Hormuz. Europeans, fearing a future without the American umbrella, begin to tighten the legal net around their own citizens’ freedom of movement.
Neither trend is inevitable. US institutions may yet constrain any attempt at a hasty NATO exit. European courts, parliaments and publics may push back against measures that feel too much like pre‑mobilization by stealth. But the direction of travel is clear: security is once again being used to justify a rebalancing of rights and obligations, at home and between allies.
In that sense, the real question may not be whether America actually leaves NATO over the Strait of Hormuz. It is whether the mere possibility of such a rupture has already started to change how Western democracies treat the people they claim to protect.
Disclaimer
Views expressed above are the author’s own.
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